Marine pollution is not a new problem. Plastics, chemicals, trash, abandoned fishing gear, invasive species, noise…and the list goes on. Although there is some debate about how harmful each of these pollutants may be, they are all labeled “pollution” for a reason.
Plastics, trash, and chemicals are examples of tangible marine pollution [1–3]. While the popular concept of giant “islands” of trash floating in the ocean is a misconception, these “garbage patches” do exist. However, instead of looking like the contents of a household trash container, these concentrated pollution areas are mostly comprised of tiny, fingernail or smaller sized pieces of plastic. From afar, the ocean may appear to be the same as any other area, but when filtered through a net it is apparent that some parts of the ocean are indeed littered with marine debris [1,2]. Chemical contaminants can also be somewhat easily perceived with water testing or even plain sight (e.g. oil spills). The evidence for these types of marine pollution is practically irrefutable, and there is a consensus that changes must be implemented to reduce the problem. However, what about marine pollution that we cannot see?
Humans are very visually oriented. As a species, we have constructed our terrestrial environment to favor our keen eyesight. For marine animals, however, the situation is different. The ocean is dark and vast, limiting the effective transmission of visual or olfactory signals. Thus, sound is the best sensory modality for many marine animals to communicate and perceive their environment. Although sound waves cannot be seen (by the naked eye at least), noise can be a significant source of marine pollution. Since the industrial revolution, increasing anthropogenic activities in the oceans has become a significant threat to marine ecosystems. The noise generated by oil and gas exploration, renewable energy development, shipping, and fisheries operations is a marine pollutant that is increasingly being recognized as a danger to marine life [4–8].
Unlike marine debris, noise pollution easy to “clean up” without harming marine life. As soon as a sound source is quieted, the noise is gone. For example, following the events of September 11th, 2001 the reduction of shipping traffic along the Eastern seaboard resulted in a 6dB drop in low-frequency vessel noise. During this time, researchers were able to measure stress hormone levels of North Atlantic right whales in the Bay of Fundy, Canada and they found that the drop in vessel noise aligned with a reduction of stress-response from the whales. When shipping activity resumed, stress-response levels increased, revealing that increased ambient noise has physiological consequences for whales . The results of this study demonstrate that while noise is indeed a harmful pollutant, simply controlling the amount may be an effective way to reduce its destructive impact on marine animals.
Similar to all other forms of marine pollution, the key to reducing anthropogenic noise is to inform the public and scientific community about how human activities negatively and directly influence marine animals, and then to gather support for policy and behavior reform. With research and strategic planning, I am hopeful that solutions can be brought forth to reduce all types of problematic marine pollution.
 M. Eriksen, L.C.M. Lebreton, H.S. Carson, M. Thiel, C.J. Moore, J.C. Borerro, et al., Plastic Pollution in the World’s Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea, PLoS One. 9 (2014) 1–15. doi:10.1371/journal.pone.0111913.
 M. Eriksen, N. Maximenko, M. Thiel, A. Cummins, G. Lattin, S. Wilson, et al., Plastic pollution in the South Pacific subtropical gyre, Mar. Pollut. Bull. 68 (2013) 71–76. doi:10.1016/j.marpolbul.2012.12.021.
 T.H. Hutchinson, B.P. Lyons, J.E. Thain, R.J. Law, Evaluating legacy contaminants and emerging chemicals in marine environments using adverse outcome pathways and biological effects-directed analysis, Mar. Pollut. Bull. 74 (2013) 517–525. doi:10.1016/j.marpolbul.2013.06.012.
 A.D. Davidson, A.G. Boyer, H. Kim, S. Pompa-Mansilla, M.J. Hamilton, D.P. Costa, et al., Drivers and hotspots of extinction risk in marine mammals., Proc. Natl. Acad. Sci. U. S. A. 109 (2012) 3395–400. doi:10.1073/pnas.1121469109.
 B.S. Halpern, K.A. Selkoe, F. Micheli, C. V Kappel, Evaluating and ranking the vulnerability of global marine ecosystems to anthropogenic threats., Conserv. Biol. 21 (2007) 1301–15. doi:10.1111/j.1523-1739.2007.00752.x.
 C. V Kappel, Losing pieces of the puzzle: Threats to marine, estuarine and diadromous species, Front. Ecol. Environ. 3 (2005) 275–282. http://nova.wh.whoi.edu/palit/Kappel_2005_Frontiers in Ecology and the Environment_Losing pieces of the puzzle Threats to marine, estuarine and diadromous species.
 A.J. Read, The Looming Crisis: Interactions between marine mammals and fisheries, J. Mammal. 89 (2008) 541–548. http://nova.wh.whoi.edu/palit/Read_2008_Journal of Mammalogy_The Looming Crisis Interactions between marine mammals and fisheries.
 R.M. Rolland, S.E. Parks, K.E. Hunt, M. Castellote, P.J. Corkeron, D.P. Nowacek, et al., Evidence that ship noise increases stress in right whales., Proc. R. Soc. B Biol. Sci. 279 (2012) 2363–2368. doi:10.1098/rspb.2011.2429.